(1) Field of the Invention
The present invention relates to a method and apparatus for producing wood particles or fibrous elements of a uniform size from wood pieces through impact comminution controlled by separating extraction mechanics from disintegrating mechanics. In particular, the present invention relates to a method and apparatus for comminuting wood pieces where the wood pieces are propelled by an impeller into contact with a first impact plate which causes cleavage of the wood pieces producing smaller wood pieces. Depending upon the weight of the remaining wood piece and the resulting wood pieces, the pieces are either impacted against a second plate for further comminution or are drawn upward out of the apparatus by a negative air flow mechanism.
In the lexicon of the smaller wood elements derivable from wood, the terms: flake, strand, splinter, sliver, fiberbundle and fiber are associated with definite products into which they are composed. Each element contributes characteristics to the composite and to its processing in accordance with the element's geometry. The fibrous strand or fibrous element is a combination element being composed of both a strand-like element and fiber-like elements. The strand part may be straight but is usually bent or curved. The fibrous parts are partially cleaved appendages that branch off in random directions from the strand part.
Fibrous strands, like other wood elements, can be produced and have utility over a wide range of sizes. Fibrous strands are three-dimensional particles, compared to two-dimensional flakes, and one-dimensional slivers or splinters. Strands (actually narrow flakes) as used in Oriented Strand Boards (OSB) are strictly speaking, two-dimensional but are used in a one-dimensional manner (oriented) to create strength in a given direction.
The three-dimensional configuration of the fibrous strand contributes uniquely to its further processing and to the properties of the resulting composite material. Unlike flakes and other linear or flat elements that depose themselves parallel to the surface upon which they fall, fibrous strands assume a more random orientation. Thus, flakes contribute strength primarily in the x-y plane, leaving the z plane relatively weak. Fibrous strands, however, because of their more random orientation, produce substantially greater strength in the z plane. The z plane figures heavily in the performance of overlays and in the general integrity of the composite material.
Fibrous strands also compose themselves into a rather open but cohesive mat. Such a mat is easy to transport between operations, is easily infused with gases, liquids and powders, has less edge defects in pressing, produces strength perpendicular to faces, (high internal bond) and allows low, as well as high density composite materials to be made.
The three-dimensional configuration of fibrous strands confers versatility in consolidation to many types of products. Flat, molded or post-formed commodities or consumer products can be made, sometimes with the same composition. Properties are related to density which can range from about 8 pounds per cubic foot upward, depending upon the pressure applied during consolidation.
(2) Description of the Related Art
The related art has shown various types of comminuting apparatuses that involve hammermill action or impact action. Illustrative are U.S. Pat. Nos. 1,636,033 to Agnew; 3,065,919 to Burkett et al; 3,794,251 to Williams; 3,899,139 to Okada et al; 4,816,075 to Gruenewald and 5,472,147 to Doppstadt and also "Williams Hot Hog Shredders" Bulletin 871, and Hawkensen Enterprises brochure: Schutte Model 1390 Wood Grinder Hammermill.
Agnew describes an impact grinder which uses centrifugal force to throw the material radially outward at high velocity whereby the impact of the individual particles of the material against breaker rings causes the material to be shattered and pulverized into smaller sizes and extracted through a discharge spout at the bottom.
Burkett et al relates to a device for comminuting consolidated sedimentary rocks and recovering the mineral values therefrom. The machine includes a plurality of rapidly rotating, superimposed, axially-aligned discs which receive the conglomerate rock particles and throw them centrifugally and tangentially outward against an enclosing wall with an impact sufficient to comminute the particles into grains and to abrade, scour and polish the surfaces of the resulting grains to produce a valuable dust concentration which is constantly and permanently removed by downwardly flowing air.
Further, Williams and "Williams Hot Hog Shredders" Bulletin 871 show material reducing systems which use a positive air flow to move the particles through a venturi system to separate sizes.
Okada et al shows a hammermill where completely crushed matter is taken out through a screen below the hammermill and uncrushable matter is floatingly selected through ascending air currents and taken out of the housing through an exhausting route.
Gruenewald shows an apparatus for comminuting plant material for further processing. The apparatus includes an up front cutter and a shredder which are immediately adjoining and located at the end of an adjustable speed conveyor. The shredder is comprised of a series of beater tools. The shredder and up front cutter are covered by a material guide housing having several sections extending approximately vertically from the plane defined by the rotational axis of the cutter and shredder. The housing has a wall portion remote from the up front cutter and from the shredder which forms an impact and deflection baffle for the comminuted material ejected by the up front cutter for feeding this material to the shredder.
Doppstadt shows a comminuting machine having a rotary impact mechanism. A conveyor moves the material to the rotary impact mechanism which cooperates with an impact plate holding a sequence of teeth with decreasing clearance in disintegrating the material. The comminuted material is collected through comminuting grates adjacent the rotary impact mechanism.
The Hawkensen Enterprises brochure shows a wood grinder hammermill.
Also, of interest are U.S. Pat. Nos. 1,669,239 to Grindle; 3,329,350 to Wisgerhof et al and 4,087,052 to Rohrbach. Grindle shows a pulverizer for coal which uses a plurality of beating wheels of increasing diameter and thus increasing peripheral velocity to impact material against teeth for progressive disintegration. An air flow device is used to move the pulverized material from the machine through the exit port. Wisgerhof et al shows an apparatus for use in pulverizing rock using rotating blades that comminute material by combining cutting and impact. Extraction is effected through a lower port. Rohrbach describes an impact mill which stands vertically such that the grinding wheels of increasing diameter rotate horizontally at high peripheral speed to comminute friable material mainly by impact.
Only of minimal interest is U.S. Pat. No. 2,882,149 to Willems which shows a flow and mixing apparatus to improve efficiency of chemical or homogenization operations using a system of rotors and stators that produce pumping and shearing actions. Also, U.S. Pat. No. 4,701,294 to Radwanski et al which shows an apparatus for forming a fibrous web.
The art of disintegrating materials by impact forces has the general objective of reducing friable materials such as rock and coal and to some extent dry wood to a powdery or granular state. All of the currently known impact milling apparatuses introduce the material to be disintegrated at an infeed port and remove the disintegrated product through a discharge port. During transit, the material is usually subjected to increasing comminution until the final size has been reached at discharge. However, there are no means to interrupt the disintegration at intermediate stages and remove the product at some predetermined intermediate size. Moreover, it is not anticipated that these machines would accept high moisture content wood to produce a fibrous material. Without an efficient means of extracting fibrous material, which is in essence at an intermediate stage of comminution, the system becomes clogged. As a result, high moisture content wood is not a desirable feed for impact milling processes.
There remains the need for an apparatus and method for controlled impact comminution of wood pieces to produce fibrous elements from wood materials which uses an impeller to propel the wood pieces against impact plates and uses a negative air flow mechanism to remove the resulting particles or elements from the apparatus as soon as the particles or elements reach a desired size. Further, there remains a need for a wood comminuting apparatus which will permit the utilization of waste or unwanted wood to produce fiber-based, value-added products, thus providing another tool for managing our wood supply on a more sustainable and environmentally favorable basis.